1. Field of the Invention
The present invention relates to a hybrid vehicle control system, and more particularly to a hybrid vehicle control system comprising a current conversion device adapted to change an amplitude or a frequency of an alternating current generated by a generator.
2. Background Art
Heretofore, there has been known a hybrid vehicle equipped with a combination of a plurality of drive power sources and designed to be driven by operating the drive power sources simultaneously or individually depending on the situation. As a drive power source, the conventional hybrid vehicle is typically equipped with an internal combustion engine (hereinafter referred to simply as “engine”) and an electric power generator (hereinafter referred to simply as “generator”). In hybrid vehicles, a drive train configured to drive road wheels (i.e., driving wheels) only by a vehicle-driving motor is referred to as “series hybrid configuration”, and a drive train configured to selectively switch between a driving force mechanically transmitted from an engine and a driving force from a vehicle-driving motor so as to drive road wheels by a selected one of the driving forces is referred to as “parallel hybrid configuration”.
In either configuration, an electric power generated by the generator is once stored in a battery. Then, when the vehicle-driving motor is operated, the stored electric power is discharged from the battery and supplied to the vehicle-driving motor.
The above operation of charging and discharging an electric power into/from the battery has to be performed under mediation of an inverter for converting between a direct-current (DC) electric power and an alternating-current (AC) electric power, because the generator is designed to generate an electric power in the form of an AC electric power, whereas the charging/discharging of the battery are allowed only in the form of a DC electric power. During this operation, the presence of the inverter is likely to cause electric power loss, which leads to deterioration in fuel economy.
From this point of view, there has been developed a control system designed to supply an AC electric power from a generator to a vehicle-driving motor (AC motor) while maintaining a fundamental shape of the AC electric power, i.e., without AC-to-DC-to-AC conversion. The control system includes one type which comprises a current conversion device adapted to change an amplitude or a frequency of an alternating current generated by a generator.
The current conversion device can convert a waveform (amplitude, frequency and phase) of an alternating current generated by a generator, to a current waveform required for a vehicle-driving motor, without AC-to-DC-to-AC conversion, and supply the converted alternating current to the vehicle-driving motor. Thus, as compared with a control system designed to once convert an AC electric power to a DC electric power through an inverter or the like, the control system using the current conversion device can achieve higher efficiency, i.e., can facilitate improvement in fuel economy.
As one specific example, JP 2005-318731A discloses a vehicle power supply system comprising a current conversion device called “matrix converter”. This matrix converter is designed to convert an m-phase alternating current generated by a generator, to an m-phase alternating current having a current waveform required for a vehicle-driving motor. For this purpose, the matrix converter is provided with m×m bidirectional switches (e.g., if m=3, nine bidirectional switches).
However, for operating the matrix converter, it is essentially required to supply an electric power from a battery to the respective bidirectional switches. In view of promoting further improvement in fuel economy, there remains the need for minimizing electric power consumption of the matrix converter (current conversion device).